Study On The Association Of GNAS1 Gene T393C Locus Single Nucleotide Polymorphism With Idiopathic Premature Contractions And Response To β-blockade

Idiopathic ventricular arrhythmia is defined as that it failed to find any clinical evidence of organic heart disease under the current diagnostic techniques,but also ruled out metabolic or electrolyte disorders and long QT interal syndrome.It commonly refer to ventricular tachycardia(VT) and/or frequent,monomorphic premature ventricular contractions (PVCs).A majority of these arrhythmias arise from the right ventricular outflow tract(RVOT), and a few from the left ventricular outflow tract(LVOT).This is no significantly difference between genders. In the past,PVCs were considered to be benign. In recent years, We have found that frequent PVCs can induce cardiac enlargement and tachycardia-induced cardiomyopathy and can lead to left ventricular dysfunction and congestive heart failure;What's worse, idiopathic ventricular arrhythmia from RVOT can cause sudden cardiac death.That has aroused the attention of clinical physicians.Up to now,the mechanism of its occurrence is not clear.The two postulated leading arrhythmogenic mechanisms include triggered activity secondary to cyclic adenosine monophosphate(cAMP) -mediated delayed afterdepolarizations and abnormal automaticity(enhanced sympathetic stimulation). Heart rate variablity studies showed sympathetic and vagal tone balance index LF/HF significantly increased prior to the occurrence of ventricular arrhythmias.An animal model has been described that PVCs and VT suggestive of RVOT were induced by high-frequency nerve stimulation of the sympathetic input to the proximal pulmonary artery and can be terminated or reduced by esmolol. Increased sympathetic activity contribute to VT/PVCs.Cardiac sympathetic nerve endings release norepinephrine and act on myocardial cell membrane receptors,namely adrenergic receptors(AR).β-adrenergic receptor(B-AR) plays a major role in mediating the cardiac function. G protein system also plays a very important role in the cardiovascular system by receptor-G protein-effector signal transduction pathway. Gs protein a subunit can be coupled with activatedβ-AR and increase intracellular cyclic adenosine monophosphate (cAMP) by activating adenylate cyclase(AC), the former can activate protein kinase A (PKA) and trigger a series of molecules cascade in the intracellular. As we known, Gs protein a subunit gene (GNAS1) located on chromosome 20q13.2-13.3, there is a silent single-nucleotide mutations in the first 393 nucleotides of exon 5 by ATT mutation into ATC which codon isoleucine(ATT→ATC,Iie131),which led to enhance AC activity.Based on the signal transduction pathway,we dare to assume GNAS1 gene T393C locus single nucleotide polymorphism (SNP) may be the possible mechanism of idiopathic premature ventricular contractions.β-receptor blockade (β-Blockade) can effectively control the sympathetic nerve-related ventricular arrhythmias, including exercise-induced arrhythmia, acute myocardial infarction, perioperative arrhythmia and heart failure related arrhythmia, and can prevent cardiac death. Most ofβ-Blockade are effective in reducing PVCs counts, so we further explore the possible relationship between GNAS1 gene T393C locus SNP and the efficacy ofβ-blockade to patients with idiopathic PVCs.To determine the association between GNAS1 gene T393C loci SNP and idiopathic PVCs in Chinese Han population,and uncover the possible molecular genetic mechanism. Study the possible relationship between GNAS1 gene T393C loci SNP and the efficacy of B-Blockade on idiopathic PVCs and to exproe the genetic basis of the efficacy of B-Blockade.318 patients were screened from in-patients and out-patients in the southern hospital from January 2007 to November 2009.All samples were divided into two study groups. The Case group included 156 subjects,62 males and 94 females,mean age 48.87±14.65 years,range 18-75.The inclusion criteria:①Arrythmias noted on resting 12-lead electrocardiogram (ECG),24-hour Holter monitoring, telemetry monitoring,or during exercise stress testing as well as symptomatic ventricular arrhythmias refractory to medical therapy. The number of PVCs>30/hour, frequent,monomorphic PVCs showed bigeminy or trigeminy, with or without non-sustained ventricular tachycardia.Non-sustained VT was defined as VT≥3 beats and lasting<30 seconds;②Hypertension,Coronary atherosclerotic heart disease(CHD), Dilated cardiomyopathy,Hypertrophic cardiomyopathy,Arrhythmogenic right ventricular cardiomyopathy,Valvular heart disease were excluded by ECG,Chest Radiography,Transthoracic echocardiography, Biochemistry,Myocardial enzyme,and some of by three-dimensional imaging coronary angiography and Coronary angiography;③Hereditary arrhythmia such as Brudaga syndrome,long/short QT syndrome were excluded;④Ruled out sick sinus syndrome, atrioventricular block and other bradyarrhythmias;⑤Ruled out electrolyte disorders and metabolic diseases such as rheumatoid arthritis and diabetes. The Control group included 162 subjects,65 males and 97 females,mean age 50.39±12.84 years,range 18-75.The inclusion criteria:no ventricular arrhythmias or the number of PVCs<30/hour, Comply with the above exclusion criteria and matched in gender,age,body mass index(BMI),smoking, drinking with the case group.Both groups were set up clinical data sheet. Basic clinical datas include age, sex, height, weight, BMI, smoking, drinking.24-hour Holter monitoring was tested in all of the subjects and record the total number of 24-hour PVCs,average heart rate,SDNN,SDANNindex, SDNNindex,rMSSD,pNN50, LF, HF and LF/HF. In fasting state, venous blood was collected in all subjects,EDTA anticoagulant. Genomic oligodeoxynucleotide (DNA) in leukocyte extracted by DNA Extraction Kit. T393C locus in exon 5 of GNAS1 gene were analysed by polymerase chain reaction-restriction fragment length polymorphism(PCR-RFLP).Distribution of T393C genotypes and alleles were compared between the two groups,as well as the relation to heart rate variability(HRV).96 patients from the case group were chosen without bronchial asthma, chronic obstructive pulmonary disease, peripheral vascular disease and suitable forβ-Blockade and can take medicine regularly. Betaloc tablets start at small dose,increase gradually to 25mg,2 times/day.Monitor adverse reactions such as orthostatic hypotension,sinus bradycardia, atrioventricular conduction block and so on. They were followed up for 4 weeks. Compare the number of PVCs after medicine and analysis the possible relationship between GNAS1 gene T393C locus SNP and the efficacy ofβ-Blockade.1.GNAS1 gene T393C locus SNP exists in Chinese Han population by PCR-RFLP.2. The frequencies of genotype of TT, TC, CC in case group was 46,78,32 and 67,77,18 in control group. The difference between the two groups was statistically significant (χ2= 7.719, P=0.021). The frequencies of FokI-allele, FokI+allele was 54.5%,45.5% in case group and 65.1%,34.9% in control group, the difference was statistically significant (χ2=9.487,P=0.006).FokI+allele frequencies in case group was higher than control group.3.Compared to TT genetype, CC homozygous, TC+CC genotype significantly increase the risk of idiopathic PVCs. The odds ratio(OR) are 2.589(1.300-5.156),1.686(1.059-2.685),P values are 0.007,0.028, respectively.The OR values (95% CI) of heterozygous genotype TC is 1.475 (0.904-2.408), but the P value is 0.12.4. The median of LF/HF between the case group and the control group are 3.01 and 2.64 respectively.The difference between the two groups was significantly(the mean rank of LF/HF are 173.60 vs 145.93, P= 0.007).5.Among the genotypes TT,TC,CC, the difference of LF/HF is statistically significant (χ2=7.135, P=0.028).The mean rank of them are 158.12,150.55,190.38 respectively,that is CC>TT>TC.But SDNN, SDANNindex, SDNNindex, rMSSD, pNN50, LF and HF among the three genotypes was no significant difference (P>0.05).6. Metoprolol significantly decreased average heart rate and PVCs counts.The rate of significant effective,effective and ineffective are 38.5%,32.3%,29.2%, respectively. In the significant effective group,the frequencies of genotype TT,TC,CC are 10,11,16 and the frequencies of FokI-allele, FokI+allele are 41.9%, 58.1%;In the ineffective group the frequencies of genotype TT,TC,CC are 15,9,4 and the frequencies of FokI-allele, FokI+allele are 69.6%,30.4%; Comparison of the significant effective group and ineffective group,the distribution of genotypes and alleles are significant.χ2 values are 7.294,9.878 and P values are 0.026,0.002. CC genotype in the significant effective group was significantly higher than ineffective group.1.GNAS1 gene T393C locus SNP exists in the Chinese Han population.2.LF/HF is significantly higher in case group than the control group and sympathetic nerve activity increased.3.The T393C polymorphism of GNAS1 may be associated with idiopathic PVCs in the Chinese Han population, Fokl+allele may be the predisposing factor.4. There is a clear correlation between GNAS1 gene T393C loci SNP and LF/HF,that is CC>TT>TC.5.The underlying mechanism of idiopathmic PVCs caused by T393C locus SNP: The Fokl+allele variant of the Gs protein may be associated with a functional variant that enhances activation of AC activity,resulting in increased cAMP production and PKA activity,which increase the risk of its incidence.6.β-Blockade is effective for idiopathic PVCs by inhibiting the sympathetic tone.Their effectiveness is considerably greater in patients with CC genotype. Therefore,β-Blockade therapy should be the first choice in these patients.